Uranium monocarbide and method of preparation



Patented Aug. 31, 1948 UNITED STATES TENT OFFICE URANIUM MONOCARBIDE AND METHOD OF PREPARATION Energy Commission as represented by the United States Atomic No Drawing. Application September 6, 1944, Serial No. 552,932

3 Claims. 1

This invention relates generally to uranium alloys and more particularly to uranium carbides. More specifically, our invention is concerned with the reduction of uranium oxides by carbon and the formation of uranium carbides of low carbon content, such as uranium monocarbide, UC, uranium dicarbide, U02, and uranium sesquicarbide, U203, having less than about per cent carbon. Uranium carbides of low carbon content have structural strength and resistance to wear superior to uranium metal or uranium oxide. In some applications of uranium forms these properties are desirable and the use of a uranium carbide is advantageous.

It is an object of our invention to provide a process for the preparation ofuranium carbides of low carbon content and particularly the mono-, di-, and sesqui-carbides of uranium.

Another object is to provide a process for the production of these uranium carbides in massive form having a high density non-porous structure free of voids.

In the process of the present invention either uranium dioxide. (U02) or uranium tritaoctaoxide (U308) may be used as a supply of uranium for the formation of uranium carbide. Uranium oxides are converted to-uranium carbides by reaction with carbon at elevated temperatures, and we have found that a low concentration of carbon in a mixture with uranium oxide will reduce all of the oxide and form a carbide. The uranium carbides produced thereby may be the monocarbide, dicarbide, or sesquicarbide depending upon the proportions of constituents in the initial mixture.

Broadly, these uranium carbides of low carbon content may be prepared by first comminuting uranium oxide and carbon to a fine powder and mixing the two powdered substances, maintaining in the mixture a relatively low percentage of carbon. The powdered mixture may then be placed in a crucible and heated in a furnace to melting or nearly to melting causing a reaction of uranium oxide and carbon to take place whereby the desired carbide is produced accompanied by the evolution of carbon monoxide. The con Version of uranium oxide to low carbon uranium carbides may also be achieved by applying heat to a compressed mass. For example, the production of uranium carbides may be achieved by pressing the uranium oxide carbon mixture and then reacting the oxide and carbon in the compressed mass by heating it in the temperature range of from l750 to 2375 C. and belowthe melting point of the uranium carbide formed.

The melting points of the uranium carbides are of the order of 2350 to 2400 C. for uranium dicarbide and uranium sesquicarbide, and 2250 to 2300 C. for uranium monocarbide. During this reaction the uranium oxide is reduced by the carbon and uranium carbide is formed. The heating of the pressed mass causes a sintering of the particles which causes the carbide produced to become more compact. The extent to which this sintering takes place depends upon the temperature and the period of heating, and the degree of sintering is increased by higher temperatures and longer heating periods. Therefore, the density of the uranium carbide produced is determined by the temperature at which the heating is carried on and the length of the period of heating. In general, it is preferable that the manufacture of uranium carbides be achieved from uranium dioxide, although uranium tritaoctaoxide may also be used to form carbides of low carbon content following the procedures outlined herein.

The carbon content of a uranium carbide formed by our process is directly related to the proportions of the components in the mixture of uranium oxide and carbon from which the carbide is produced. By ascertaining the relation between the quantitative ratio of the parts of uranium oxide and carbon in the initial mixture and the percentage composition of the uranium carbide produced, then it is possible to produce uranium carbide with a predetermined percentage of carbon by the selection of proper proportions of the components in the initial mixture.

We have discovered that in the formation of uranium carbides from uranium oxide by reduction with carbon, the quantities of oxide and carbon reacting with each other to form a particular carbide may be predetermined from the stoichio-metric ratios of the chemical reaction involved, wherein all of the oxygen of the par ticular oxide used is converted into carbon monoxide. In forming' a uranium carbide the reactants are mixed in about the stoichiometric ratio of the equation of the reaction for the particular carbide desired. As a result it is possible to predetermine the carbon percentage of the uranium carbide produced, by adjustment of the proportions of the oxide and carbon in the initial mixture.

As an example. uranium monocarbide may be formed by mixing uranium dioxide and carbon and heating this mixture. The production of the uranium monocarbide with its low carbon content is achieved by proportioning the parts of uranium dioxide and carbon in the reacting mixture, and by carrying on the reduction of the oxide by the carbon so as to reduce all the oxide with the formation of carbon monoxide and combine all the uranium and carbon, leavin no residual carbon or uranium dioxide. Uranium monocarbide is formed from uranium dioxide and carbon in conformance with the following equation:

UOz-l-3C UC+2CO In this equation the stoichiometric ratio of uranium dioxide to carbon in the initial mixture of-the components is 5.6261. The uranium dicarbide produced according to the above equation has a carbon content of about 9.16 per cent. The preparation ofuranium sesquicarbide from uranium dioxide and carbon by'the process of thepresent invention follows the equation:

2'UO2+7C- U2C3+4CO In thisreaction the stoichiometric ratio of uranium dioxide to carbon is6;43:1. When-departs of uranium dioxide are mixed with one'part of carbon and heated according to this invention,' A

the uranium sesquicarbide'produced will have'a carbon content of about 7.03 percent.

The 'density'and porosity of the mass of' uranium carbide producedby melting or agglomeratiii'g can be varied and controlledby'theparticle size "ofthe uranium oxide and carbon. The preparation of a uranium carbid'e'froma'mixture of uraniumdioxide or uranium tritaoctaoxide isinstituted by first grinding up and sieving the uranium oxide and'the carbon "and'then mixing the powdered components. 'Byg-rinding'the uraoxide and carb'ontoapowder thatwill'pass "fine mesh screens of'the order of 100'mesh or finer, accurately shaped and less porous "uranium carbide may be produced.

Where'the conversion reaction ist'o takep'lace in a carbon or'g'raphite crucible, somewhat less ith'anthe stoichiometricpercentage of'carb'cn may be used in view of the fact that same of the crucible material may react with the uranium to 'form'acarbide. 'Itis also desirable in some-cases to addextra uranium oxide to thecruciblewhen the reaction between the carbon and uranium oxideof the original mixture is nearlycomplete.

The following examples illus'trate'specific embodiments of our invention as applied'totheproduction-of' uranium carbides of low carbon-content, but it is to be understood that similar results may be obtained by modified procedures'without departing from the spirit of this invention;

Example 1.7.5 parts by weight ofuranium-dioxide finely powdered to pass through a lOO mesh screen are mixed with one part of similarly-fine graphite. about 26 tons per square inchto the form-of a' bar The mixture is first pressed under /2 x x 2" having a density of 7 grams per cubic centimeter, and the bar is stood on end in a graphite crucible to prevent appreciable reaction of the mixture with the graphite of the crucible. The bar is then heated slowly to the range of 2275 C. to 2320 C.', and the temperature maintained in this range for 20 minutes. An alloy with uranium and carbon in the ratio of U1C1.27 is produced. This product is the compound UC containing some carbon dissolved or dispersed therein.

Example 2.5.7 parts by weight of uranium dioxide powdered to pass a mesh screen are mixed in an iron mortar with one part of graphite pow'dere'cl'tov pass a 200 mesh screen. The mixture is inductively heated in a graphite crucible at 'about 9.5 kilowatts for 15 minutes and 12 kilo- Watts for 50 minutes. The product is a compact .mass of uranium carbide having crystals radiating away from the center of the mass, Carbon analyses made on samples from this mass indicate an average of 9.15 per cent carbon which approximates thetheoretical 9.16 per cent carbon in UC2.

Example 3. 362.5 grams of graphite are mixed with 2037.5 grams of uranium dioxide and heated in a graphite crucible to a temperature between 2100 C. and 2300 C. while the conversion reaction takes place. After the reaction is-completed, the temperature is raised to about 2500 C. The product is a mass of uranium dioarbide free of gas pockets and-with a density measurement of 10.8 grams per cubic centimeter.

Example 4.'7 .9 parts by Weightof uraniumdioxide powdered to pass a 100 mesh screen are mixed inan iron mortar with one part of graphite powdered to pass a 200 mesh screen. The .mixture is heated in a pure graphite crucible, as much as possible being packed in at. the beginning, and the remainder being added after. the reaction begins. The heating is carriedon. at about 9.5 kilowatts for 15 minutes, .andat about 12 kilowatts for 50 minutes. The productis a-well formed mass which analyzes to give 7.21 per cent carbon indicating the formation of the -dicarbide and the sesquicarbide.

Example 5.-8 parts by weight of'uraniumdioxide are mixed with one part of carbon. The mixtureis heated in a crucible in an induction furnace to give a compact mass containin uranium sesquicarbide with an overall density of 11.5 grams per cubic centimeter.

Example 6.-7.5 parts byweight ofzuranium dioxide are mixedwith one part of graphite. The mixture is heated in a crucible in an. induction furnace. Amass including uranium..sesquicarbide crystals is produced in awell-sliaped form.

Although the reactions. of.uranium.dioxide.have been used to illustrate the application of the process of the present invention, other methods within the spirit of this inventionmay be used to obtain uranium carbides. Uranium dioxide may be melted in agraphite crucible, when heated quickly to'avoid reaction withthe crucible, and uranium dicarbide chunks. added to the melt. The product is uraniumdicarbide, 'duetothereaction of the. uranium-'dioxidewith the graphite of the crucible walls.

Thus'we have been able, bY'fOIIOWingthBTDI'OCBSS described and claimed'herein, to 'consistentlyrproduce uranium-carbon alloys having a predetermined carbon content of less than about 10 per cent.

While theforegoing embodiments" of ourinvention have been discussedv as .performed in an air atmosphere, a hydrogen atmosphere has also been found suitable.

Numerous variations and modifications in the preferred methods and examples described will be readily apparent and may be made without departing from the spirit and scope of our invention as defined in the following claims.

We claim:

1. A method of forming uranium monocarbide which comprises heating to reaction temperature a mixture comprising an oxide of uranium and carbon in substantially stoichiometric proportions required for monocarbide.

2. A method of forming uranium monocarbide which comprises heating to reaction temperatures a mixture comprising U02 and carbon in substantially stoichiometric proportions required for monocarbide.

3. Uranium monocarbide having the compositiOn UC.

HARLEY A. WILHELLL ADRIAN H. DAANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,017,558 Winter et al Oct. 15, 1935 2,364,123 Benner et a1 Dec. 5, 1944 OTHER REFERENCES Chemical Abstracts, vol. 8 (1914), article by Tiede et al., page 2855, line 11, 

